1. Field of the Invention
The present invention generally relates to the gallium-nitride based light-emitting diodes and, more particularly, to an epitaxial structure of the gallium-nitride based light-emitting diodes having a high reverse withstanding voltage and a high resistivity to electrostatic discharge.
2. The Prior Arts
Gallium-nitride (GaN) based light-emitting diodes (LEDs), as various color LEDs can be developed by controlling the GaN-based material's composition, has been the research and development focus in the academic arena and in the industries as well in recent years. Besides being applied in the display of consumer electronic appliances such as digital clocks and cellular handsets, technology breakthroughs in terms of luminance and lighting efficiency has led GaN-based LEDs into applications such as outdoor display panels and automobile lamps.
To have practical applicability in these outdoor display devices, besides having high luminance and lighting efficiency, GaN-based LEDs must have a rather high reverse withstanding voltage and high resistivity to electrostatic discharge (ESD), so that they can continue to operate for an extended period of time under the harsh, outdoor environment.
However, for conventional GaN-based LEDs, they have a traditional epitaxial structure by growing GaN-based nitrides on a sapphire substrate. GaN-based nitrides and the sapphire substrate usually have mismatched lattice constants, causing an excessive accumulation of stresses and, thereby, causing the GaN-based LEDs to have an inferior epitaxial quality. The GaN-based LEDs' anti-ESD capability and reverse withstanding voltage are therefore deteriorated.
The most widely adopted solution in recent years is to use a flip-chip process to combine a GaN-based LED with a Zener diode made of silicon. Although this solution indeed effectively improves the GaN-based LED's anti-ESD capability, the flip-chip process is much more complicated than the traditional manufacturing process for general GaN-based LEDs.
Accordingly, the present invention is directed to overcome the foregoing disadvantages of conventional GaN-based LEDs of the prior arts.